Friend or Foe?

Invasive species

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Protecting ecosystems from non-native species has been a priority among ecologists and conservationists since at least the 1980s. Horror stories such as the Burmese python slithering around the Everglades swallowing endangered birds, the Asian carp decimating native fish populations in the Great Lakes, or kudzu taking over just about everything are, in fact, worrisome. But do all non-natives deserve a bad rap? Aren’t ecosystems dynamic by nature? Mark Davis says biologists and government officials need to be more careful about assigning blame. Daniel Simberloff argues that preventing invasions is better than trying to address them later.

Harm Is in the Eye of the Beholder

by Mark Davis

Mark Davis is the DeWitt Wallace Professor and Chair of Biology at Macalester College, St. Paul, MN. He is the author of Invasion Biology (Oxford U Press, 2009).

For 25 years, the American public has been inundated with horror stories involving non-native species. Think: snakehead, kudzu, Asian carp. This has largely been the result of selective communication from scientists and a media that too often have been more than eager to promote these stories without engaging in any critical analysis or research of their own. Usually provided with just a single perspective, the public largely accepted the idea that non-natives, as a group, are noxious and undesirable.

In fact, this is anything but true. Non-native species are just species. Like native species, some of them produce effects we like, some produce effects that we don’t like, and most are comparatively benign. Have some introduced species caused changes that most everyone would agree have been very harmful? Absolutely. By killing timber trees, gypsy moths and the emerald ash borer have caused, and continue to cause, enormous economic damage to the United States. Introduced pathogens that threaten human health are also clearly harmful species. At the same time, the danger posed by non-native species as a group often has been exaggerated and misrepresented. For example, ecologists and conservationists often describe non-native species as the world’s second greatest extinction threat, despite the fact that existing data shows this clearly not to be the case. It is true that introduced species can and have caused many extinctions in insular environments such as oceanic islands and freshwater lakes. But they have caused very few extinctions on continents or in marine systems. In fact, the primary regional biodiversity effect of introduced species is to increase species diversity. Due to the introduction of thousands of plant species, the United States has approximately 20 percent more wild plant species than it did 500 years ago.

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